Objects can be seen after turning off all lights : How to turn off ambient light in Blender/Cycles?
In Cycles, the Background is emitting light. This will affect all objects, which receive light.

In order for the ojects to not receive additional light, do one of the following.


Set the background color to black (0, 0, 0).
[or] Set the strength property of the Background BSDF to 0.0.
[and] Disable Ambient Occlusion.




If you don't want your background to appear black, the following node setup restricts the backgrounds visibility to camera rays.

You can also restrict the visibility of the background with the cycles settings. Uncheck everything except Camera under Ray Visibility and the background emit no light except to the camera.